4.6 Ford Modular Short Blocks – A Guide to a Bottom End for Boost

Way back in 1996, Ford introduced their all new “Modular” engine in the Mustang GT and Cobra. All around the country, die-hard five liter fans hung their heads and sighed. You could take everything you knew about how to make your 5.0 Mustang faster and just throw it out the window. It was very different. It had two or four cams instead of one and no pushrods. The teeny, tiny 3.552” bore was wimpy compared to the large 4.000” bore of Windsors, 289’s, and 302’s. It had powdered metal rods, a long stroke of 3.543”, and lots of chains and tensioners under the massive timing cover. Plus, it was a measly 281 cubic inches.

It was only a matter of time before power hungry Modular owners demanded the tried and true bolt-on power adders. The power adder companies responded quickly with supercharger, turbocharger and nitrous kits. Today there are literally hundreds of different ways to boost more air through the small 4.6 displacement and get really big torque and horsepower numbers.

Tim Matherly from MV Performance decided to build a supercharged Modular engine for NMRA Real Street competition because “that’s what all my customers have – blown Modular engines.” He knows that for his 4.6 Ford to last round after round, he has to have a good bottom end.

It turns out that not only do Modular engines work basically the same way as their pushrod counterparts, but they respond very well to any type of forced induction. The only issue they seem to have (with the exception of the factory supercharged engines), is that they simply are not built to handle the large amounts of power that everyone is easily squeezing out of them! Which leads us to the topic of this article: How to get a stronger bottom end Modular engine.

It is not uncommon now to look under the hood of any Modular powered Mustang and see a big bad blower bolted to the top of the engine. The Modular short blocks in these cars must be boost friendly.

Piston Problems

The Ford Modular engines were and are designed for efficiency and reliability – naturally aspirated. That means that most of them have coated hypereutectic pistons for their low expansion, tight piston to wall clearance, and reduced weight. This is great if you are leaving it stock, but awful if you add too much boost. That’s because the aluminum alloy used contains a lot of silicon for lubrication, but the silicon creates weak spots throughout the piston, especially under detonation. These hypereutectic pistons tend to shatter like glass when subjected to too much heat or cylinder pressure.

The fix is a nice set of forged aluminum pistons, preferably 2618 alloy. This low silicon aluminum is much stronger and will hold up to much more heat and detonation without failure. Under extreme conditions the forged slugs can still fail, but they tend to do minimal damage by simply starting to melt instead of exploding.

Today there are several manufacturers who offer quality pistons, each with their own benefits. Manley Performance has their Platinum Pistons in a variety of dish volumes, from flat-top to 23cc, which include coated skirts and offset wrist pins to reduce noise. Ross and JE Pistons each offer 2618 aluminum pistons that feature CNC machining in several different configurations as well. But, if you are looking at making big boost, the top of the line is the ModMax/CP forged pistons. These are beefed up in the dish and pin boss areas specifically for power adders and have super flat ring grooves for the best ring seal. They are also offered in standard, .020”, or .030” over sizes. Keith Black has now come out with a quality affordable forged 2618 piston for Modulars as well, that are a great choice at a lower price.

It is now time to take a look at the compression ratio. Big boost engines like lower compression than the higher ratio factory pistons yield. A good choice is between 9 to 9.5:1 with up to 12psi of boost, and 8.2 to 9:1 with over twelve pounds. As boost increases, the effective compression ratio also increases, so lowering the ratio allows more boost and more timing, which makes the engine easier to tune and typically makes power with less chance of detonation. Depending on which cylinder head is used, the dish volume will vary as each head has different combustion chamber volumes as well as the newer 3V heads, usually requiring a piston with a valve relief. The bottom line is to get a piston matched for the power level and use of the engine.

Three-valve 4.6 Modulars require slightly different pistons than the two or four-valve engines. These CP/ModMax shelf pistons are built for boosted late model three-valve engines with the addition of a special valve notch.

Plasma moly rings are typically available from each of the piston manufacturers and are necessary to hold up under higher cylinder pressures. The material holds tension better and the moly face coating is plasma welded to the ring to endure higher temperatures. Although durable, the moly is only good up to a certain power level. Moly tends to chip off the edge of the ring under very extreme temperatures and detonation. For engines that may run higher boost or on the edge of detonation, a steel top ring is preferred. The steel rings are machined, not cast like plasma moly, and hold tight tension after many heat cycles. These are typically about double the price of moly rings, but are the most durable and are necessary with Modulars over around 15psi of boost.

A Strong Connection

Unless you have an ’03-’04 Cobra engine, the factory supplied connecting rods just simply aren’t designed to hold up to any big power. The factory two-valve engines had cracked cap powdered metal rods that are typically not even resizable, with naturally aspirated Cobra engines utilizing a forging. Many of these are also only set up for pressed pins. Fortunately, there are many choices on the market now to upgrade the weak arms for strength.

The factory 4.6 base engines have powdered metal, cracked cap rods. The minimum upgrade would be strong set of forged 5140 steel I-Beam rods like these pictured from ModMax. They are fully machined, have bronze bushings for full floating pins, and are held together with ARP 8740 cap screws.

If you aren’t looking to make over 550 flywheel horsepower, the ModMax 5140 forged I-beam rods are a great upgrade. They are fully machined, with bronze bushings for floating pins, and ARP fasteners. For more serious applications, there are a variety of forged 4340 material H-beam rods on the market from ModMax, Manley, SCAT and others. However, they are not all the same, so pay attention to the details regarding the bolts. They can be supplied with ARP 8740 or ARP 2000 material cap screws, with a strength advantage going to the ARP 2000 bolts. The H-beam rods will usually support up to around 750 flywheel horsepower with the 8740 bolts, and over 1000 horsepower with the better ARP 2000 bolts. All the H-beam rods are quite strong, with bronze bushings, and are very reasonably priced.

For all out competition use with huge amounts of boosted air, the Modular engines should be utilizing some type of billet connecting rod. Manley, ModMax, and Oliver all have excellent top shelf choices for 4.6 engines with ARP 2000 cap screws or equivalent holding them together. The 4340 material on billet rods are fully CNC machined from a block of steel to exacting tolerances. These are all made with the I-beam design for light weight and will withstand 1500 plus flywheel horsepower and over 9000 RPM. Although these rods cost quite a bit more than H-beam rods, the price is well worth it for no failures on maxed out Modular short blocks.

Choosing rods for a good 4.6 bottom end means looking closely at the bolts the rods are using. 3/8″ diameter 8740 material bolts are good up to around 700 horsepower or so, but for more power and RPM, most rod manufacturers offer an ARP2000 material bolt upgrade.

Forging Ahead with the Crank

Having the correct crankshaft for power adders is an important part of having a strong bottom end. Most Modular single overhead cam engines came with a cast crankshaft with either a 6-bolt or 8-bolt flywheel flange. Cobra engines were equipped from Ford with a stronger forged micro steel crankshaft with only the 8-bolt flywheel pattern. The cast pieces are fine for naturally aspirated and boosted applications up to around 500 flywheel horsepower, but when building the short block for strength, it is obvious that the forged steel crank is preferred.

A forged crankshaft for 4.6 Modulars is just what the doctor ordered if big power plans are in the future. Note: the forged pieces do not have any seams or parting lines. Plus the radiused journals offer greater strength in the throws of the crank. If using a factory 4.6 GT block, clearancing will be necessary to make room for the center counterweights found on forged Modular crankshafts.

With the majority of the engines out there containing the cast part, seeking out a forged crank is relatively easy. Ford Racing and ModMax both have brand new stock stroke forged cranks right on the shelf for immediate purchase. The forged cranks are not only forged from higher strength steel, they also feature undercut radii on the rod journals for superior strength. Usually these cranks can support over 1000 horsepower without failure. Just keep in mind that when upgrading from a 6-bolt cast crank, it is mandatory to also purchase an 8-bolt flexplate or flywheel to work with the new forged crankshaft.

If a crank is on the list of upgrades, this may be a good time to look at increasing the stroke. The stock stroke is 3.543” yielding 281ci with a standard bore, but ModMax offers a 3.750” crank that increases displacement to 302ci with a .020” overbore. Since the cost of the crank is only slightly more, and ordinarily the other components like pistons, rods, rings, and bearings are about the same, it can be a wise investment to increase the cubic inches. With either stock or stroker forged cranks, it is also important to check the clearance for the center counterweights. Aluminum 4.6 blocks already clear the extra center counterweights on the forged cranks, however stock cast iron blocks will need to be machined for fitment as the cast units do not have the center counterweights.

It may not cost much more when already purchasing pistons, rods, rings, bearings, and/or a crankshaft to go ahead and increase the stroke on a 4.6 short block. A stroker kit makes matching up parts easier, as special pistons and rods must go along with the 3.750″ stroke crankshafts.

Building Blocks

A good strong bottom end can be based on a number of OEM or aftermarket Modular blocks. All dual overhead cam 4.6 engines came with an aluminum block from Ford, with the exception of the ’03 to ’04 Cobra engines, because Ford engineers believed the cast iron Romeo block to be a stronger choice for the supercharged Mustang. Most two-valve Modulars were built with either a Windsor or Romeo cast iron block, with slight differences between the two blocks. Windsor engines were supplied in most trucks, with the ’99-’00 Mustang GT also utilizing that version of the cast block. Romeo cast iron blocks were predominantly used in passenger cars from ’96-’98, as well as ’01 and up, including the ’03 to ’04 Cobra.

Ford Racing now offers both aluminum and steel “BIG BORE” blocks for 4.6 rebuilds. The aluminum version (part number M-6010-T50 pictured above) is the same one used in the Ford 5.0L Cammer engines. A cast iron version is available as part number M-6010-BOSS50.

There has been some controversy over whether the Ford aluminum block is strong enough for big horsepower, although it seems as though any of the factory blocks are plenty strong enough for high performance applications. The important thing to remember when building for power are that the bores must be straight and true, which typically means overboring .020” to .030” (the maximum recommendation on factory blocks) and buying the appropriate pistons to match.

For larger gains in cubic inches (in addition to the stroker cranks mentioned above), there are a few options to run larger bore sized blocks for the 4.6 Modulars. There are a few aftermarket companies that offer big-bore sleeve kits for aluminum factory blocks to increase the bore up to 94mm (3.700”). These kits can be installed into an existing aluminum block by a quality machinist or can be purchased already done in block form. In addition, Ford Racing now offers both cast iron and aluminum blocks with the larger 94mm bores that are brand new and designed for performance. Although pricey, this big bore does help unshroud the valves for more airflow, especially on single overhead cam cylinder heads. The bigger bore, combined with a stock stroke, increases the 4.6 liter to 305 cubic inches and 323 cubes when combined with a 3.750” stroker crank. Note that when switching to the much larger 94mm bore size, it is also necessary to use larger bore head gaskets that are available from Ford Racing and Cometic.

Combining a big bore of 3.700″ with a 3.750″ stroker crankshaft can make one mean and nasty 4.6 based engine. From the outside, it looks like a standard Modular 4.6, but inside it displaces 323 cubic inches!

It is important to note that most of the blocks offered can use all the available 2V, 3V, or 4V cylinder heads when combined with the proper timing components, tensioners, and timing covers. However, when choosing bearings for the block, the proper application must be used on the main bearings. There are at least three different sets of bearings for aluminum, Romeo, or Windsor blocks that have different tang locations and thrust bearings. So, when choosing the block for performance, it is mandatory to assemble the accurate parts to go with the specific components used.

Bearings for 4.6 short blocks are specific to the block being used on the mains. Windsor, Romeo, and aluminum blocks all take different main bearing sets, with different thrust washers, flanged bearings, and tang locations. The King bearings shown here are offered in a high performance version for all three variations.

Completing the Bottom End

In addition to the blocks, cranks, rods, and such, there are a few small items that can finish off a great Modular short block. All of the factory main bolts are designed to be torqued only once, so a set of ARP main studs are a wise investment. They are not only reusable, but also distribute the clamping force on the main caps as well as reduce cap distortion.

Why spend all the money on a built 4.6 bottom end and use factory bolts? ARP main studs are available for all blocks, with or without windage tray mounts. The studs are a wise option for maintaining good, even torque.

Another wise choice is an improved oiling system using an aftermarket high pressure and/or high volume performance oil pump. Melling manufactures pumps that are available with billet steel gears that hold up under all conditions without breaking. Both Melling and Ford Racing also offer pumps that increase volume and pressure for the additional RPM and bearing stress that performance engines endure. When the oiling volume is increased, it is also a good choice to add an aftermarket oil pan with additional capacity so the pan is never dry. Plus, the aftermarket pans also control sloshing and windage, keeping the oil in the pickup area under acceleration.

Melling offers both 2V and 4V specific performance pumps with chrome moly billet steel gears. The 2V version pictured on the right is standard volume and uses the stock 13/16″ diameter pickup tube on SOHC engines. The 4V pump on the left is standard volume for DOHC engines using a 15/16″ diameter pickup tube but can also be used on 2V Modulars to increase volume.

It’s a Mod Mod World

Luckily, the Modular engine was not snubbed by the aftermarket world, and performance seeking enthusiasts now have many choices when it comes to improving 4.6 engine power. With so many options regarding blocks, pistons, and rods, anyone looking to make their overhead cam Ford hold up with turbos and blowers can easily just surf the web and get everything from individual parts to a fully built short block. Of course, as racers have been embracing the Modular engines, even more parts can be custom made. Billet crankshafts of any stroke, custom low drag pistons, and even aluminum rods can be purchased now to hold up to 1800 plus horsepower. So, choose your weapon of choice: big bad blower, twin turbos, or huge nitrous, and sleep easily knowing that a bullet proof short block is only a click away!